This invention relates to the field of gas monitoring.
The invention provides a method and apparatus for wireless monitoring of gases, including toxic and combustible gases, with a device that has a radio transmitter that transmits quantitative gas levels to a master controller or multiple master controllers.
Toxic gas monitoring systems are well known. Generally, gas monitors are placed around chemical producing facilities such as a chemical processing plant. These monitoring systems are configured to monitor for the presence of toxic and/or combustible gases. In addition to monitoring for the presence of these gases, typically in parts per million or lower explosive limits, these detectors could be configured to detect other important information such as wind speed and direction, temperature and other weather conditions. This information is then relayed to some sort of central reporting system. For instance, the information can be relayed back to the control center of a chemical plant and be displayed on a computer terminal or information sent directly to the plant""s Distributive Control System.
Conventional toxic gas monitoring systems usually comprise multiple sensing units. These units are placed in and around the perimeter of a chemical processing plant, for example, to constantly monitor the targeted conditions around the plant. Upon detection of a toxic gas, usually at a predetermined level, the unit may sound an alarm in addition to relaying the information to the control center. This information can be used, for example, to determine the source of the gas so that an unexpected leak can be corrected. Alternatively, should the plant simply be operating at too high of a capacity and thus be generating too much toxic waste, its operations can be brought to within acceptable tolerances. Additionally, the wind speed, weather conditions and direction of the gas can be used to determine which people need to be warned about the presence of toxic gas and when such a warning should be issued.
Typically, in gas detection systems a master site provides information to a computer. U.S. Pat. Nos. 5,553,094, 5,568,121 and 5,771,004 disclose such systems. U.S. Pat. No. 5,597,534 discloses a circuit that measures a chemical sensor output. Typically, specially designed software is incorporated as well. For example, the Gastronics"" Event Scada Software is an unlimited tag Scada software which runs off Windows 95, 98 or 2000 or Windows NT and is designed for user friendliness along with the ability to customize and map out the geography of a plant. The Event Scada Software offers the user the flexibility to design and customize individual screens to match different applications. An assortment of tools allows the creation of trend charts, wind speed and direction, alarm settings and maintenance screens. A multilevel security feature may be included to prevent unauthorized access to customization functions.
Currently, the method of relaying this important information from the monitors to the control center has been through wires which physically connect each of the monitors to the output system. This is generally referred to as xe2x80x9chard wiring.xe2x80x9d Hard wiring requires each monitor to be physically connected to the output system by some sort of wire or cable. Hard wiring each of the numerous monitors to the control system can be quite costly, cumbersome and require substantial and frequent maintenance. For example, should the output system ever need to be relocated, such as in a different control room or outside of the plant, the cables would need to be rerouted to this new site. Rerouting all of the cables is labor intensive and expensive.
To further complicate matters, the wires may need to be buried in the ground (typically below the frost line) to comply with building code requirements or simply as a precautionary measure. Burying multiple wires in the ground requires substantial excavation which is rarely inexpensive. Similarly, repairing, replacing or moving these wires also requires substantial, expensive excavation.
Alternatively, the wires may need to be suspended at a height substantially above ground level. Such suspension may require the installation and maintenance of some sort of suspension devices, such as telephone poles. These poles would be placed in and around the chemical plant. This, again, may be an expensive undertaking. Finally, with regard to hard wiring, the wires themselves are usually expensive and are prone to breaking, cracking or failing in some sort of way. Thus, it is apparent that a wireless toxic gas monitoring system is desirable. The present invention comprises such a wireless toxic gas monitoring system.
It is common to monitor gas levels around large plants. Additionally, it is not uncommon for gas monitors to be placed some distance from these large plants. Consequently, the monitors may have to transmit information a substantial distance. Moreover, because the destination of this information is often located somewhere deep within the plant, e.g., a central control room, the monitors may need to relay this information through physical objects, such s layers of concrete, steel, insulation and other building materials.
In addition to physical barriers, the monitors usually need to transmit the information through substantial interference as well. Electric equipment and communication systems existing in almost all plants create vast amounts of interference such as electromagnetic waves, for example. Thus, a wireless gas monitoring system that is able to transmit information over a substantial distance and through substantial amounts of interference is desirable. The current invention utilizes, but is not necessarily limited to, licensed radio frequencies that operate at higher powers and are therefore able to transmit over large distances and through substantial amounts of interference.
Radio telemetry has recently been used as a lower cost alternative to hard wiring the monitors to the output or control systems. A typical radio telemetry system using RTU""s, while reducing significant installation costs, still requires both the high cost of the RTU as well as the installation costs to wire the gas monitors to the RTU. With the advent of the current invention, the advantages of wireless toxic gas monitoring systems are realized. This particularly true with respect to very long conduit runs, such as with perimeter monitoring applications, where the cost of the RTU and wiring the sensors to the RTU is increased by the long lengths of the conduit and installation costs.
Additionally, most monitors of the related art are event triggered only. By this it is meant that the monitors only relay a signal when they detect a high level of gas. The monitors merely let you know when a threshold level of gas (such as a gas denoted xe2x80x9calphaxe2x80x9d) has been surpassed. For instance, if a system were set to detect 0.5 ppm of gas alpha but a dangerously high level of 20 ppm of gas alpha existed around the plant, the detector would only transmit a signal telling the controller that an amount of gas alpha above 0.5 ppm had been detected. However, the actual concentration, i.e. the dangerously high 20 ppm of gas alpha, would not be relayed back to the control room. This type of system would not provide and quantitative documentation which may be useful in any number of situations.
Thus, a wireless gas monitoring system with heightened sensitivity is desirable. By this it is meant that it would be desirable to have monitors that monitor and relay more detailed information. The current invention does just that. The monitors will not only relay the actual amount of gas detected, i.e. 20 ppm, but they may also relay operating parameters of the system such as the battery voltage, day, date, time, wind speed, weather conditions, etc. existing at the time the gas was detected.
From the foregoing it is clear that certain improvements are desired. Many of the desired improvements have been accomplished by the current invention.
The present invention contemplates a new and improved method and apparatus for wireless gas monitoring which is simple in design, effective in use, and overcomes the foregoing difficulties and others while providing better and more advantageous overall results.
The current invention is a system for wireless toxic gas monitoring with a monitoring device that eliminates the RTU by integrating the radio transmitter directly into the gas monitor, thus making it integral with the device. Although the current invention may utilize licensed UHF radio transmissions, the device is not limited to the type of radio, whether it be land based, cellular or satellite, the strength or radio or any safety approval classifications.
The transmitters feature a unique method of wireless monitoring that eliminates not only the high installation costs of hardwired systems, but also the cost of wireless Remote Terminal Units (RTU""s). A typical perimeter gas monitoring system, where the monitors are completely hardwired to the master site, costing in the neighborhood of $400,000 may only cost $200,000 if the monitors are hardwired to RTUs and the RTUs transmit via radio to the master. The current invention which has the transmitters integral with the monitors would reduce the cost of this system to approximately $100,000 by eliminating the RTU""s and the associated costs of installation and installation materials.
One advantage of the current invention is that the licensed radio frequencies enable the current invention to operate at higher powers. This allows the monitors of the current invention to transmit information over large distances and through substantial amounts of interference.
Another advantage of the current invention is the fact that it is wireless. This permits toxic gas monitoring and installation to be performed in an inexpensive manner not requiring substantial and frequent maintenance.
Yet another advantage of the current invention is the fact that remote transmitters are integrated into the monitors of the current invention. This enables equipment, maintenance, labor, manufacturing and installation costs and expenses to be reduced.
Still another advantage of the current invention is the fact that each of the monitoring devices and the output center may comprise a transceiver. The transceiver can both transmit and receive messages. Separate transmitters and receivers are therefore not needed and costs are thereby reduced.
Another advantage of the current invention is its heightened sensitivity. Upon detection of a gas, the monitors monitor and transmit a substantial amount of detailed information.
Still other benefits and advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed specification.
A plurality of gas monitor stations are provided at locations which are spaced from a potential source of a selected gas whose presence is to be detected. Each of the gas monitor stations includes a gas sensor assembly, a control assembly, a radio, and data entry apparatus. The data entry apparatus may be a keypad which is manually actuated. However, the data entry apparatus may include magnetically actuated switches and/or a remote control unit. A display is provided at each gas monitor station to provide for visual review of data entered at the gas monitor station.
In response to a predetermined condition, radio transmission to a master station is initiated from any one of the gas monitor stations. The predetermined condition which results in initiation of radio transmission may be one or more of a plurality of different conditions. The conditions which result in initiation of radio transmission may be varied by actuating the data entry apparatus to change data stored in the control assembly at each of the gas monitor stations.
The conditions which result in initiation of radio transmission from any one of the gas monitor stations may include one or more of the following conditions:
(a) Sensing of a predetermined concentration of the selected gas in the atmosphere at the gas monitor station.
(b) Sensing of a predetermined change in the concentration of the selected gas in the atmosphere at the gas monitor station. The change in the concentration of the selected gas may be either an increase or a decrease in the concentration of the selected gas.
(c) The elapse of a predetermined maximum length of time since the last radio transmission was made.
(d) Determining that a moving average of sensed concentration of the selected gas exceeds a predetermined magnitude.
(e) Determining that a battery, which supplies current for the radio, has an output voltage which is less than a predetermined voltage.
(f) A change in battery voltage by a predetermined amount.
It should be understood that the data entry apparatus at each of the gas monitor stations may be utilized to select any one or more of the foregoing conditions or other conditions not set forth above, to initiate radio transmission from a gas monitor station while omitting other conditions. The data entry apparatus may also be utilized to enter data corresponding to parameters, that is, limits, utilized in association with each of the conditions which initiate radio transmission from a gas monitor station to a master station. The sensor assembly at each of the gas monitor stations may be calibrated by exposing the sensor assembly to a known concentration of the selected gas. This may be done by exposing the sensor assembly to a container of gas or gas-generating device, such as a permeation tube calibrator or gas generator. The data entry apparatus is actuated to adjust data set forth on a display at the gas monitor station to correspond to the known concentration of the selected gas.
Once the sensor assembly has been calibrated, the sensor assembly may be checked by applying a predetermined voltage to the sensor assembly.
In order to eliminate the effect of transient conditions, such as puffs of the selected gas, the sensor reading at a gas monitor station is averaged over a predetermined period of time. This period of time may be relatively short, for example, thirty seconds or less. The predetermined period of time over which the sensor readings are averaged may be entered into the control assembly by actuating the data entry apparatus at a gas monitor station.
It should be understood that anyone of the features of the invention may be used separately or in combination with other features. It should be understood that features which have not been mentioned herein may be used in combination with one or more of the features mentioned herein.